1971 challenger front disc: I replaced the passenger front caliper once because the caliper wasnt functioning properly. So i installed a new one after about 5000 miles the same problems started happening. Car pulls to the left when braking because the passenger caliper isnt engaging. And when it does decide to engage it will ocassionally lock up. What are the odds that 2 calipers just happen to go bad?

Its possible but not probable. Check and if necessary replace your brake lines on that side, sound to be like its got an obstruction or junk floating around in there that is combining to stop pressure being applied. It might even be more up stream to the distribution valve.

When I bled the brakes on the passenger side the fluid runs through clean. I've replaced the line from the prop valve and the flex hose on this side pretty recently. I just replaced the caliper yesterday, 25 bucks at discount auto. Seems to be working correctly....for now.

Its a pretty simple system, so long as there are not any obstructions in the line, there is adequate fluid, no air in the line and good mechanical parts (i.e. good caliper and straight rotor) its going to work.

I know and it drives me crazy that i'm having such a problem with it. the caliper replacement seems to be doing to job. If i have even a sneeze of a problem i'll be purchasing the MBM conversion kit. Both sides new spindles, rotors, calipers, bearings, flex hoses. $400 for peace of mind not a bad price IMO.